Electric resistance welding



0d- 8. l940- G. HAGEDORN ELECTRIC RESISTANCE WELDING F1104 50121,.,28, 1938 3 Sheets-Sheet l Oct. 8. 1940. G. HAGEDoRN 2,217,546

ELECTRIC RESISTANCE WELDING Filod Sept. 28, 1938 5 Sheets-Sheet 2 ffy Oct. 8, y1940- cs. HAGEDoRN 2,217,545

ELECTRlC- RESISTANCE WELDING F1104 Stpt. 28, 1938 3 Sheets-f-Sheei 5 90 i r /79 j d l @L/"ra Patented Oct. 8, 1940 UNITED STATES ELECTRIC RESISTANCE WELDING Gerhard Hagedorn, Berlin-Halensee, Germany,

assignor to Bernhard Berghaus, Berlin-Lankwitz, Germany v Application September 28, 1938, Serial No. 232,195

, In Germany October 9, 1937 4 Claims.

'I'he present invention relates to a method of electric resistance spot welding and more particularly pertains to such welding wherein circulating currents are induced in superimposed 5 parts of the material to be Welded together.

In carrying out the invention eddy currents are induced in the material to be welded and such currents are produced by a coil arranged between the points to be welded and alternating current having a frequency of about 300 to 20,000 cycles is supplied to the coil for short periods of less than one second down to about onethousandth of a second. Pressure is applied to the material to be welded together by means of nonconductors or pressure pins which carry no current. The pressure is preferably transmitted by two or more neutral pressure pins from a pressure transmitter to the work to be welded. The current transitions which are point-like or have a small surface between the parts to be welded together, for instance, two metal sheets, may be favourably influenced by the impression of indentations or by the insertion oi? metal layers having a small surface. Use is preferably made of frequencies which lie beyond the normal network frequency of 50 or 60, preferably 300 to 20,000 cycles per second, short periods of welding, which lie b'elow one second down to about M000 of a second being employed. v

The invention is illustrated diagrammatically, and by way of example, in the accompanying drawings, in which A Fig. 1 is a partial section of the whole apparatus for electric resistance spot welding, more particularly double spot welding without electrodes with magnet coil and control of the welding time;

Fig. 2 is a section through the welding pressure indicating device according .to Fig. 1;

Fig. 3 is a diagram of connections of a device controlling the period of welding;

Fig. 4 is an elevational View of a device with another arrangement o! the magnet coil;

Fig. 5 is a side view of the device according to Fig. 4;

Fig. 6 illustrates a further arrangement of the magnet coil for double spot welding without electrodes;

Fig. 7 is a side view of the device according to Fig. 6;

Fig. 8 illustrates a further arrangement for double spot welding without electrodes, in which use is made of one electro-magnet;

Fig. 9 is an elevational view of the arrange- 55 ment shown in Fig. 8.

Fig. 10 is an elevational view oi a further arrangement for single spot welding without electrodes and Fig. 11 shows a doublev spot welding arrangement without electrodes applied to metal sheets' with indentations.

Referring to Fig. 1 which shows a partial section of the whole of the apparatus for electric resistance spot welding, more particularly double spot welding without electrodes with magnet coil and control of the welding period, I and 2 are the two metal sheets to be welded together, which are shown cut out in the plane of the welding points in order to illustrate the operations in this plane. On the metal sheets to be welded together there are placed two pressure pins 3 and 4, which are electrically neutral and are arranged a certain distance apart. 'I'he pressure pins are, for instance, secured to a plate 5, which is, in its turn, connected to a plunger B the upperv part 1 oi' which is connected to a lever l provided with a handle l, which the welding operator grips to produce the desired pressure, read on the pressure gauge I0 by means of the indicator II. l

By exerting the point-like pressure by means of the two pressure pins 3 and l, two point-like zones of small transition resistance are produced between the two metal sheets underneath the pins. The transition resistance between the two metal sheets is indirectly proportional to the pressure with which they are pressed against one another. 'I'he alternating magnetic ileld produced by means of the magnet coil I2 fed by an alternating current generates eddy currents or circular currents I3 in the two metal sheets I and 2 to be welded together, which follow a closed circuit through the upper metal sheet I, the one pressure point, the lower metal sheet 2, the other pressure point, and back to the upper metal sheet I. 'I'hese circular currents iiow through the point-like zones of small transition resistance, producing two welding spots Il and II at these places. The arrangement shown is especially suitable for the production of welding spots which are not too far removed from the edges of the metal sheets. The magnet coil I2 is controlled from the source of alternating current I 6 over a switching device consisting, for instance, of switching vessels Il, I8. I9 and 20 are two controlling grids in the switching vessels, which are controlled by the mechanical or electrical control impulse transmitter 2I. The control is eiected by ,means of the pedal switch 22, which is connected by means of a rod 23 with the 55 switch il. i5 is a condenser which serves to compensate the idle current.

Referring to Figure 2, which shows a section through the welding pressure indicating device according to Fig. i, Ii is the indicator connected to a ger-.r wheel 26 which engages in teeth 21 provided in the upper part 1 of the pressing plunger. The upper part of the pressing plunger rests ou a springr 28, which, in its-turn, is

i mounted in the part of the pressing plunger l constructed es a bearing 2B, wh in a casing 30, preferably' masi Referring to Fig. 3, which shoe.

' supplied with current from the alternating current network 3i. l5 is the secondary coil of the transformer and 36 is an adjustable resistance in the excitation circuit. Further, a controlling transformer 4l is fed with current from the alternating current network 3| over a transformer 31 and an adjustable resistance Il, which serves for phase displacement, and a saturated choking coil H. 4l is a resistance, 42 and 4I are adjustable reslstances which are connected to the grids, and

1% i4 are the secondary windings of the transformer I0. l5 and 46 are voltage bias batteries, which siuply the stopping voltage, and l1 and 4I are adjustable rcsistances. l! is a short circuiting `witch for the controlling transformer, which, by

means of a. relay consisting of a magnet coil Il and an iron core 5i, is drawn into the magnet coil 50, when current flows through the latter thereby opens the short circuiting switch of the controlling transformer. 22 is the pedal switch mentioned in connection with Fig. l, which is connected to a switch 2l through a rod Il. 52 ic u battery for charging the condenser Il. which may be discharged through an adjustable reststsnce 54 and the magnet coil Il. The time Y l1 thus consists of a relay II, 0| and timing which is constituted by a condenser and .hie resistance. By regulating the re- 54 any desired short adiustment of the Leiding is rendered possible.

eti-lod according to the invention it is age to make the time of the iiow of short .as possible, firstly, because the e. thc-n netter from a metallurgical point new, and, secondly, because the heat losses Fiuther, .according to the invention n advantage to use an alternating current 1 has a periodicity greater than the usual 1w frequency of 50 or 80 periods. Thus, for lusts-nce, use is made of middle or high fref ouencics, preferably of 300 to 20,000 cycles per second. In this way, it is possible to concentrate n re energy on a smaller space, and in addition to e comparatively small capacity is then for the compensation of the idle power. y currents, which are otherwise prothe Field in the metal sheets, effect an moderate heating of the immediate the material. By dispensing with the welding electrodes connected to a transformer all their disadvantages and dimculties, such as cooling, good contact, careful subsequent treatment, damage to the surface of the metal sheets are avoided l in the improved spot welding method.

Referring to Figs. 4 and 5. which show a double spot welding device with a modified arrangement of the magnet coll. i and l are the metal sheets to be welded together, Il and are the pressure pins arranged on the pressure member Il. which has, for instance, a projection Il on which the magnet coil Il rests. Il and Il are the two welding spots and indicates the path of the circulating current. The magnet coil in this 1I arrangement is moved out towards the top out of the plane of the metal sheet and forms an angle therewith. The inclination oi the axis of the `coil with respect to the plane of the metal sheets is required and is an advantage, since the mag- I netic lines of force are at right-angles to the surfaces of the circular currents induced in the metal sheets and the planes of the paths of current should be as much as possible at right-angles to the surface.

As shown in Pigs. 6 and 'l the magnet coil may be also arranged as a solenoid Il, with its axis in the direction of the plane of the metal sheets, between the two pressure pins Il and Il. I and 2 are the two metal sheets and Il and l1 the two l welding spots.

Further, as shown in Pigs. 8 and 9, use may be made of a magnetic circuit, which is partly ironclad. landlareinthiscasethemetallheets to be welded together, Il and Il are the pressure pins, Il is a laminated iron core, 'Il and 12 are the field coils of the magnets and Il and 14 are the welding spots.

Further, in the case of the herein described double spot welding apparatus only one single 40 spot may be produced, if one of the two pressure pins is provided with a substantially larger oontact surface than the other me. Since the magnetic field intensity is limited and the value o( the magnetic flux is dependent upon the existing thickness of the metal sheets, the induced voltage and thus also the welding current, is limited. I! in the case of very thick metal sheets, the output is not sumcient, according to the invention two or more circuits are connected in parallel on the secondary side. This is eected, as is shown by Figure 10, for instance, by the arrangement ot two coils 1I and 'Il and three pressure pins Il, Ii, l2. In this way, there is produced in the metal sheets l and 2 to be welded together two circular currents Il and Il, which produce a sin- 81e welding spot Il. This multiplication may be correspondingly carried out with the other arrangements which have been described. Purther, three or more such devices may be placed one next to the other.

As shown in Pig. l1 it is especially advantageous for the method according to the present invention to press in indentatlons or bulges Il, l1 in the one metal sheet i. In this way, more especially when the material is not yet softened, the path of the current is determined more deflnitely and, moreover, the suace enclosed by the current paths is increased, so that the flux, the voltage and the power are greater.

The improved method is also suitable for seam welding and the seam may be produced by causing lapped or not lapped spots to follow one another. u

kizo

What I claim is:

1. The method of spot welding which comprises, arranging a metal sheet over another metal `sheet, applying pressure to the sheets at two points to provide lower resistance between the sheets at the points where the pressure is applied than the resistance between the sheets laterally of said points, applying an alternating magnetic eld to said sheets between said points so as to produce eddy currents which flow along one sheet to one oi! said points and then pass to the other sheet and ilow therealong to the other point before passing again to the rst sheet whereby the current passing from one sheet to the other is concentrated at said points to provide spot welds.

2. The method of spot welding which comprises, arranging a metal sheet over another metal sheet, applying pressure to the sheets at two points to provide lower resistance paths between the sheets at the points where the pressure is applied than the resistance between the sheets laterally of said points, applying an alternating magnetic ileld to both of said sheets between said points with the axis of the magnetic field arranged substantially at right angles to a line extending through said points so as to produce eddy currents which flow along one sheet to one ot said points and then pass to the other sheet and flow therealong to the other point before passing to the first sheet whereby the current flowing from one sheet to the other is concentrated in said lower resistance paths to weld the sheets together immediately under the points where the pressure is applied. y

3. 'Ihe method of spot welding which cornprises, arranging a metal sheet having spaced projections extending from a face thereof over another metal sheet, applying pressure at two points defined by the projections to provide lower resistance between the sheets at the points where the pressure is applied than the resistance between the sheets laterally of said points. applying an alternating magnetic field to said sheets between said points so as to produce eddy currents which now along one sheet to one of said points and then pass to the other sheet and now therealong to the other point before passing again to the rst sheet whereby the current passing from one sheet to the other is concentrated at said points to provide spot welds.

4. The method of spot welding which comprises, arranging a metal sheet over another metal sheet, applying pressure to the sheets at two points to provide lower resistance paths between the sheets at the points where the pressure is applied than the resistance between the sheets laterally of said points, applying an alternating magnetic field to both oi said sheets between said points with the axis o! the magnetic field arranged substantially. at right angles to a line extending through said points and with the axis of the magnetic iield arranged 'in the contacting plane o! the two sheets )between said points so as to produce eddy currents which flow along one sheet to one of said points and then pass to the other sheet and flow therealong to the other point before passing to the tlrst sheet whereby the current flowing from one sheet to the other is concentrated in said lower resistance paths to weld the sheets together immediately under the points where the pressure is applied. u

GERHARD HAGIDORN. 

